1. Field of the Invention
The present invention relates to an optical communication device in an optical communication system such as a telephone exchange system and in particular, the present invention relates to an optical communication device including a main shelf with unit plates having optical modules and a sub-shelf with optical fiber supporting plates.
2. Description of the Related Art
Recently, optical fibers have often been used in telephone communication systems, for example, between regional telephone exchange stations. The telephone exchange unit includes, as a part thereof, an optical communication device comprising unit plates including electronic components and optical modules. The optical modules are optical-electrical converters that receive optical signals from optical fibers and convert them into electrical signals, and also receive electric signals and convert them into optical signals for transmittance by optical fibers. Electrical signals are treated within the exchange unit.
Connectors are attached to the ends of optical fibers that are not cut near the end thereof and usually have surplus length portions near the ends thereof that are considerably longer than the length necessary to achieve a connection between the optical modules and thus the surplus length portions are coiled in a freely extendable manner in situ.
Japanese Unexamined Patent Publication (Kokai) No. 3-171796 discloses an optical communication device including unit plates having optical modules in which optical fibers having surplus length portions coiled in a freely extendable manner are connected to the optical modules. In this prior art, unit plates are arranged in the shelf of a housing parallel to each other in upright positions. A bundle of the optical fibers introduced in the housing and coiled surplus length portions of the optical fibers are rested on top of the shelf and the ends of two optical fibers are connected to each of the optical modules.
Recently, optical communication has developed and the number of unit plates with optical modules per one optical communication device has increased. Also, optical fibers are used between the unattendant center and telephone subscribers. In this case, numerous optical modules and optical fibers are necessary, and when many unit plates with optical modules are housed in one optical communication device, a problem occurs in that the optical fibers may be incorrectly connected to the optical modules if the coiled surplus length portions of the optical fibers are layered one above the other out of order.